(1) Field of the Invention
Molecular complexes showing spin transition phenomena have been the subject of fundamental research since their discovery in 1931. Since then approximately three hundred complexes have been synthesised and studied using different physical-chemical techniques. The spin transition phenomenon can be initiated by temperature, pressure (G. Molnar et al., J. Phys., B. 107, 2003, p. 3149; A. Bousseksou et al., C. R. Chimie 6, 2003, p. 329), an intense magnetic field (Bousseksou et al., Top. Curr. Chem. 235, 2004, p. 65) or light (N. Ould Moussa et al., Phys. Rev. Lett., 94 2005, p. 107205; S. Bonhommeau et al., Angew. Chem. Int., Ed. 44, 2005, p. 2) and is accompanied by a change in magnetic, optical and/or electrical properties. This phenomenon has been physically modelled and is well understood (A. Bousseksou et al., Eur. J. Inorg. Chem., 2004, p. 4353). From the point of view of applications a number of interesting prospects have been suggested (O. Kahn et al., Science 279, 1998, p. 44; O. Kahn et al., Chem. Mater. 9, 1997, p. 3199; O. Kahn et al., Adv. Mater. 4, 1992, p. 718). In particular thermal hysteresis of the dielectric constant in the course of spin transition has been discovered (FR 0111328, EP1430552, A. Bousseksou et al., J. Mater. Chem. 13, 2003, p. 2069), thus making it possible to design micro-nano-condensers having the property of storing information on the molecular aggregate scale.
(2) Description of Related Art
Using the physical properties of inorganic and organometallic complexes generally requires placing these compounds as a thin layer on a substrate and, if necessary, micro- or nano-structuring into elements of submicron size. The difficulty in this lies in compatibility between the product and the process of deposition, because spin transition is a phenomenon which is very sensitive to various disturbances of the crystal lattice.
So far two methods of deposition have been suggested:                the method known as the Langmuir Blodgett method, which consists of preparing a film by transferring a single layer floating on a liquid onto a solid support. This method can however only produce a two-dimensional monolayer; this is inadequate for most applications because (1) it is difficult to detect hysteresis cycles in a monolayer (particularly in the case of a deposit on a small surface area) and (2) maintenance of the hysteresis cycle is not ensured in the case of a single monolayer.        The method known as “spin coating”, which consists of depositing a fluid on a support by centrifuging (spinning plate), followed if appropriate by evaporation of the solvent. However the spin transition material is deposited in the form of a mixture with an inactive matrix, generally a polymer. Mixing of the active material with the matrix may be discontinuous and generally gives rise to a non-homogeneous deposit. In addition to this, dissolution of the material in the matrix causes loss of the crystalline lattice. These disadvantages therefore limit the use of this process.        
There is therefore at the present time no method through which a thin layer of spin transition complexes can be deposited as a thin layer while maintaining the properties of spin transition, hysteresis and a surface condition of acceptable quality. It is therefore particularly desirable to provide a process for the deposition of spin transition complexes as thin layers which will fulfil these requirements.